The present invention relates to an image capturing unit for an electronic endoscope which is built in at a distal end portion of an insertion section of the electronic endoscope.
Generally, the image capturing unit for the electronic endoscope is configured such that a solid-state image capturing element is held by a holding frame. The solid-state image capturing element is configured such that, on a front surface having an image capturing surface, boding wires are arranged at peripheral positions thereof to extend in outer directions, The solid-state image capturing element is held at a tip portion of the holding frame. Further, a transparent cover glass is air-tightly attached to the front end (tip end) of the holding frame so that steam or water does not enter even when the endoscope is placed inside a high-temperature high-pressure steam sterilizer or the like. Examples of such a configuration are disclosed in Japanese Patent Provisional Publications Nos. P2003-100920A and HEI 07-226493.
FIG. 6 shows an example of a conventional image capturing unit for the electronic endoscope. In this example, a cover glass 93 is directly cemented onto the tip end surface of a solid-state image capturing element holding frame 92 that holds the solid-state image capturing element 91. In FIG. 6, 91a denotes an image capturing surface, and 94 denotes each of the bonding wires.
When the image capturing unit 90 as shown in FIG. 6 is implemented in an objective optical unit 80 including an objective optical system 81 as shown in FIG. 7, if a distance A between the image capturing surface 91a and the cover glass 93 is relatively large, a back focus B necessary for focus adjustment with respect to the objective optical system 81 becomes relatively short, and it sometimes becomes impossible to perform sufficient focus adjustment.
On the other hand, if the back focus B is increased with the distance A remained unchanged, it becomes necessary to increase the entire length of the insertion section of the endoscope. When the insertion section becomes long, it becomes difficult to insert the insertion section in a human cavity, and further, such a configuration has a bad effect on a basic performance of the endoscope.
Therefore, it is preferable to make the distance A as short as possible. However, if such a configuration is employed and the optical system is manufactured, due to unevenness of sizes, thickness and the like of components, the cover glass 93 may contact the bonding wires 94 as shown in FIG. 8. In such a case, the bonding wires 94 may be damaged.
FIG. 9 shows another example of a conventional image capturing unit for the electronic endoscope, in which the cover glass 93 is air-tightly cemented with a cover glass holding frame 95, which is air-tightly cemented with a solid-state image capturing element holding frame 92.
In this configuration, as shown in FIG. 10, if the distance A between the image capturing surface 91a and the cover glass 93 is reduced to avoid a problem when the image capturing unit 90 is assembled in the objective optical system unit 80, the cover glass 93 may contact the bonding wires 94 as shown in FIG. 11. Therefore, also in this case, the bonding wires 94 may be damaged.